A wide variety of implantable medical devices (“IMD”) that deliver therapy to or monitor a physiologic condition of a patient have been clinically implanted or proposed for clinical implantation in patients. Such devices may deliver therapy or monitor the heart, muscle, nerve, the brain, the stomach or other organs or tissues. In some cases, IMD's deliver electrical stimulation therapy and/or monitor physiological signals via one or more electrodes or sensor elements, at least some of which may be included as part of one or more elongated implantable medical leads. Implantable medical leads may be configured to allow electrodes or sensors to be positioned at desired locations for delivery of stimulation or sensing electrical activity or other physiological parameters. For example, electrodes or sensors may be located at a distal portion of the lead. A proximal portion of the lead is coupled to an IMD housing, which contains electronic circuitry such as stimulation generation and/or sensing circuitry. In some cases, electrodes or sensors are positioned on an IMD housing as an alternative or in addition to electrodes or sensors deployed on one or more leads.
One example IMD is an electrical stimulation device directed to nerve tissue stimulation, which is sometimes referred to as an implantable nerve stimulator or implantable neurostimulator (“INS”). One particular application of nerve tissue stimulation is vagal nerve stimulation. Vagal nerve stimulation may provide therapeutic effects for heart failure, as well as other conditions including, e.g., depression, epilepsy and various digestion conditions. Some vagal nerve stimulators, as well as nerve trunk stimulators in general, have employed cuff electrodes to surround the nerve tissue and anchor the stimulator lead and/or electrodes within a patient. Cuff electrodes have some disadvantages, however, including, that such electrodes require relatively invasive techniques for placing them within a patient. In the case of vagal nerve stimulation, cuff electrodes require an incision in the neck and dissection of the vagus from within the carotid sheath for placement around the nerve. Additionally, cuff electrodes are known to cause lesions or otherwise damage the nerve tissue, which may lead to deleterious effects on nerve function, as well as the development of scar tissue.